The present invention relates to a device for supporting a mobile part which moves relatively to a loadbearing part.
In prime movers and driven machines, for example, water turbines and pumps, the mobile part comprises the shaft of the rotor, and it usually is mounted in two or more bearings. In the past, these bearings have been so dimensioned that they can accept the forces which occur during normal operation and also the dynamic forces which are encountered occasionally. These dynamic forces occur, for example, during starting and stopping of the machine and when changing between driving and driven modes of operation, and they may be a multiple of the normal forces. Therefore, the bearings must be very rigidly constructed. As a result, powerful forces caused by temperature fluctuations can be developed in the bearings, and these too may have a magnitude which is a multiple of the normal bearing loads.
The object of this invention is to provide an improved mounting arrangement for the mobile part which permits the use of bearings which are dimensioned to accept substantially only the forces encountered during normal operation. According to the invention, this object is achieved by providing a supporting device which includes a support element which adjoins the mobile part and is oriented to accept the dynamic forces, and a hydraulic control means which responds to the rate of displacement of the support element and serves to vary the supporting force it furnishes. Under normal operating conditions, which may produce slow displacements, the support reaction is constant and relatively small. However, when a rapid displacement occurs, the reaction is substantially increased or decreased, depending upon the direction of movement. The new supporting device is not a bearing in the true sense of the word, because it performs no substantial supporting function unless the mobile part is suddenly displaced. However, since it does accept the dynamic forces when they occur, it relieves the true bearings of this burden and allows them to utilize an elastic construction. Therefore, the bearings are simpler, and consequently less expensive, to construct, and, since they are subjected to less intensive stress, they will operate more reliably.
The hydraulic control means employed in the supporting device comprises a positive displacement control motor having a movable control element which responds to the pressure in a working space which is connected with a constant pressure source via a throttled conduit. The control element is subjected to a constant pressure force as long as it moves slowly and does not change the volume of the working space at a rate which exceeds the flow capacity of the throttled conduit. However, when that element is moved rapidly, the pressure in the working space, and consequently the force developed on the movable element, will rise or fall drastically, depending upon the direction of movement. The control element of the control motor is coupled with the support element in such manner that their movements tend to correspond, and the pressure force acting on the control element determines the reaction furnished to the mobile part by the support element. Various arrangements of the components are possible. For example, in one embodiment, the support element is a hydrodynamically lubricated bearing segment, and that segment is carried directly by the movable element of the control motor. In other embodiments, the support element is a hydrostatic supporting piston which carries the mobile part without physical contact and which is urged toward that part by its own hydraulic supporting motor. In these versions of the invention, the control element is indirectly coupled with the support element, either through a spring which reacts between them, or through a valve which serves to alter the pressure in the supporting motor and has coacting members actuated, respectively, by the two elements. Regardless of which construction is employed, the throttled conduit of the control means may include a shut-off valve which can be closed to hydraulically lock the control element of the control motor, and thus prevent reestablishment of the normal support reaction, in situations, such as change-over operations, where the dynamic forces act over a relatively long period of time.